6533b823fe1ef96bd127f40e

RESEARCH PRODUCT

Ecological genetics of a cyclical parthenogen in temporary habitats

subject

description

Populations of the rotifer Brachionus plicatilis inhabiting three temporary ponds in Torreblanca Marsh (Castellon, Spain) were regularly screened for allozyme variation, sexual reproduction levels and population densities during an annual cycle. Relevant ecological parameters in the ponds were also recorded. The electrophoretic survey of the three ponds (Poza Sur, Poza Norte and Canal Central) revealed a high level of overall genetic polymorphism in four marker loci, but only 13 multilocus genotypes were found. We classified clones into three clonal groups (SS, SM, L) characterized by unique arrays of alleles in the four marker loci, and significant differences in body shape and size. Clonal group succession took place in Poza Sur; SM clones occurring in spring, SS clones from spring to fall, and L clones from fall to spring. Despite the partial overlapping of sexual periods, the absence of heterozygotes indicates that gene flow is strongly restricted between clonal groups. In the transition periods, the population was far from Hardy—Weinberg equilibrium due to hetereozygote deficiencies in all four markers. In clonal group L, the only polymorphic locus, Pgi, was in Hardy—Weinberg equilibrium. In clonal group SM, both polymorphic loci were in Hardy—Weinberg equilibrium in Poza Norte, but not in Poza Sur. Factor analysis on the limnological parameters recorded during field sampling indicates that genetically different clonal groups are also ecologically specialized. These findings suggest that the taxonomical species B. plicatilis is in fact a species complex. The complete genetic discontinuity model of rotifer population succession is supported by these data. Our results are similar to those found in cladocerans inhabiting temporary habitats.